The invention relates to bright film technology. In particular, the invention is a bright metallized formable film laminate that has superior optical and deformation properties. In a preferred embodiment, the formable film laminate includes a layer of discontinuous indium islands deposited on a polyvinylidene difluoride film. The invention is also an improved method of making bright metallized film laminates.
Metallized polymeric finishes can be used to complement and even replace bright, reflective metal surface treatments, particularly chrome plating. Polymeric structures having metallized finishes are commonly used as substitutes for articles, such as automobile grills, that are expected to have a chrome-plated appearance. Decorative polymeric components, in fact, are becoming standard in the automobile industry, primarily because plastics are relatively flexible, corrosion-resistant, and inexpensive. Plastic parts also reduce vehicle weight, which enhances performance, especially fuel economy.
Many patents disclose metallized substrates. For example, U.S. Pat. No. 5,035,940, for an Aluminum-Fluoropolymer Laminate describes a polymer-backed aluminum substrate with a weather-resistant polymer coating. Similarly, U.S. Pat. No. 5,536,539, for an Injection Molded Plastic Article with Integral Weatherable Pigmented Film Surface describes an automotive component formed from a molded polymer article having a decorative polymeric film surface. Both of these patents are commonly-assigned with the present invention.
As will be known by those familiar with the metallizing arts, chrome plating is perhaps the most common method of metallizing three-dimensional substrates, such as injection-molded substrates. Unfortunately, chrome plating not only carries onerous environmental concerns, but also introduces possible human health hazards.
A better method of metallizing polymeric substrates is to coat metal onto molded substrates, usually by vacuum deposition. In this regard, indium has gained acceptance as a preferred metal because on a microscopic scale it tends to form small, discrete deposits or xe2x80x9cislands.xe2x80x9d When bent or flexed, discontinuous metal layers tend to retain the desired optical properties better than do continuous metal films, which tend to fracture. Discrete metallization also minimizes electrical conductivity, which can hasten unwanted corrosion. For example, U.S. Pat. No. 4,431,711, for Vacuum Metallizing a Dielectric Substrate with Indium and Products Thereof addresses indium metallizing three-dimensional articles in a way that minimizes electrical conductivity and, consequently, corrosion.
In most cases, the metallized layer is covered with a transparent polymeric coating that physically and chemically protects its surfacexe2x80x94a so-called xe2x80x9cclear coat.xe2x80x9d Although in-situ metallization of formed polymeric articles is useful, it requires separate applications of a base coat, a metallized layer, and a clear coat. This necessitates drying time for each application, which lengthens the processing times (and hence costs) associated with metallizing three-dimensional articles. Therefore, depositing metal directly onto an article only after the article has been formed can be disadvantageous.
Alternatively, metallized film laminates (i.e., adhesive tapes) that can be applied to polymeric structures offer certain advantages over conventional in-situ metallization techniques. For example, metallized film laminates can be manufactured, stored, and shipped in roll form. Such laminates also facilitate customized application, limited only by adhesive effectiveness. Moreover, using a metallized film laminate reduces chemical compatibility problems that can arise between the metal and the polymeric substrate when metallizing articles in-situ.
To manufacture a metallized film laminate, a polymeric substrate is typically coated with a desired metal, often via vacuum deposition. Then, a polymeric clear coat is added to the metallization layer using conventional techniques, such as casting or doctor-blade applications. Using such metallized film laminates, though convenient, can result in an inferior finish as compared to that obtained by in-situ techniques. Therefore, it is desirable to achieve a finish similar to an in-situ process, yet with the convenience of a film laminate.
To that end, there are known to be metallized laminates that can be formed into desired shapes using conventional techniques. In addition, such molded laminates can be filled with thermoplastic polymer to produce a solid article having a similar bright finish as an article that has been metallized by in-situ methods.
For example, U.S. Pat. No. 4,101,698, for Elastomeric Reflective Metal Surfaces discloses a metallized elastomeric laminate that can provide a reflective metal surface finish for three-dimensional contoured shapes. In particular, the metallized layer is applied to an elastomeric film in separate, discontinuous planar segments. U.S. Pat. No. 4,115,619, for Highly Reflective Multilayer Metal/Polymer Composites discloses a bright multi-layer polymer composite formed by metallizing a thermoplastic polymer layer with a soft metal, such as indium. The metal layer is applied by conventional techniques, such as vacuum deposition, sputtering, or lamination. The metallized film can then be molded into a desired shape using conventional forming processes. U.S. Pat. No. 4,403,004, for a Sandwich Metalized Resin Laminate describes a metallized laminate formed of a thermoformable base layer that is coated on both sides with vapor deposited metal. This laminate is capable of being thermoformed to assume three-dimensional shapes.
Such formable film laminates have poor flexibility, however, often cracking when the metallized substrates are excessively deformed. Moreover, such moldable films tend to lose luster over time. This is particularly pernicious with respect to metallized indium layers, which in the presence of halogen-containing polymers (e.g., polyvinyl chloride) can undergo an oxidation-reduction reaction that converts elemental indium to indium trichloride. Finally, to the extent such moldable films are formed from continuous metallized layers, corrosion problems result.
Accordingly, a need continues to exist for a bright metallized formable film laminate that addresses these problems.
Therefore, it is an object of the present invention to provide a bright metallized formable film laminate having superior optical and deformation properties, and a method of making such formable film laminates.
In one broad aspect, the invention is a bright metallized formable laminate made of a discontinuous layer of indium islands deposited on a microscopically-smooth surface of a clear coat polyvinylidene difluoride (PVDF) film. In preferred embodiments, the polyvinylidene difluoride film is formed of an alloy containing polyvinylidene difluoride and an acrylate (xe2x80x9cacrylicxe2x80x9d) polymer. An especially desirable, weatherable polyvinylidene difluoride film is the FLUOREX(copyright) fluoropolymer film (Rexam, Inc.; Matthews, N.C.) that includes about 50 percent acrylic. This indium-FLUOREX(copyright) film combination has superior, quantifiable optical and deformation properties as compared to other bright formable films.
In another aspect, the invention includes an adhesive layer placed on the surface of the discontinuous indium layer, opposite the polyvinylidene difluoride film. A thermoplastic backing layer is then placed on the adhesive, opposite the discontinuous indium layer.
In yet another aspect, a formable leveling layer may be included between the discontinuous indium layer and the polyvinylidene difluoride film. In one preferred embodiment, the leveling layer includes polyurethane. In another preferred embodiment, the leveling layer includes polyvinyl fluoride.
In still another aspect, the invention includes an extensible mask layerxe2x80x94preferably polyurethanexe2x80x94that is placed on the polyvinylidene difluoride film, opposite the discontinuous indium layer. The extensible mask layer helps to maintain gloss when the indium-metallized polyvinylidene difluoride film is stretched.
In another broad aspect, the invention is a method of making bright metallized formable laminates that include a discontinuous layer of indium islands deposited on a microscopically-smooth surface of a polyvinylidene difluoride film.
One preferred method includes casting a polyvinylidene difluoride film onto a polymeric substratexe2x80x94preferably polyethylene terephthalatexe2x80x94and then depositing a discontinuous layer of indium islands onto the polyvinylidene difluoride film. A polymeric filmxe2x80x94also preferably polyethylene terephthalatexe2x80x94is placed onto the discontinuous indium layer, and then the polyvinylidene difluoride film and the discontinuous indium layer are xe2x80x9cpress polished.xe2x80x9d Alternatively, the polyvinylidene difluoride film may be press polished before the addition of the discontinuous indium layer.
Thereafter, the polymeric film may be removed from the discontinuous indium layer and an adhesive layer and a thermoplastic backing layer may be bonded to the discontinuous indium layer, opposite the polyvinylidene difluoride film, such that the adhesive layer is contiguous to the discontinuous indium layer.
Moreover, the polymeric substrate may be removed from the polyvinylidene difluoride film, and an extensible masking layer may be added to the polyvinylidene difluoride film, opposite the discontinuous indium layer. The extensible masking layer maintains laminate gloss during forming processes.
Another preferred method includes placing a formable leveling layer on the polyvinylidene difluoride film such that the discontinuous indium layer is directly deposited on the leveling layer rather than on the polyvinylidene difluoride film. Use of a leveling layer can eliminate the need for press polishing the polyvinylidene difluoride.
The foregoing, as well as other objectives and advantages of the invention and the manner in which the same are accomplished, is further specified within the following detailed description and its accompanying drawings.